Network-enabled connectivity for disadvantaged communication links

ABSTRACT

Devices, systems and methods for providing network-enabled connectivity for disadvantaged communication links in wireless networks are described. One example method for enabling connectivity over a disadvantaged link includes receiving, by a first node of a plurality of nodes from a source node in the first frequency band in a first timeslot, a first signal comprising a message, receiving, by the first node from at least a second node in a second frequency band in a second timeslot, a second signal that is used to generate a first reliability metric corresponding to the message, and performing, based on a plurality of reliability metrics corresponding to the message and the first reliability metric, a processing operation on the message, the first frequency band being non-overlapping with the second frequency band, and a duration of the first timeslot being greater than a duration of the second timeslot.

TECHNICAL FIELD

This document is directed to collaborative wireless communicationsamongst nodes in a wireless network.

BACKGROUND

Ad-hoc networks may include spatially distributed, single-antenna,power-limited radio nodes, which may be dynamic, not fully connected,and operating in multipath fading propagation environments. These nodescan collaborate to communicate with a remotely-located radio node, whichis not reachable via straightforward communication protocols.

SUMMARY

This document relates to methods, systems, and devices for providingnetwork-enabled connectivity for disadvantaged communication links inwireless networks. Embodiments of the disclosed technology can beconfigured to provide range extension, i.e., the ability to transmit andreceive messages collaboratively to a remote node that is otherwiseunreachable by a single local radio or even by multiple radiostransmitting simultaneously in a phase-incoherent manner. Thecollaborative communication technology disclosed in this patent documentcan be implemented in various devices including wireless communicationreceivers in wireless communication systems, including, e.g., radiocommunication devices, mobile devices and hot-spots in broadbandwireless networks.

In one exemplary aspect, a method for enabling connectivity over adisadvantaged link is disclosed. The method includes receiving, by afirst node of a plurality of nodes from a source node in the firstfrequency band in a first timeslot, a first signal comprising a message;receiving, by the first node from at least a second node in a secondfrequency band in a second timeslot, a second signal that is used togenerate a first reliability metric corresponding to the message; andperforming, based on a plurality of reliability metrics corresponding tothe message and the first reliability metric, a processing operation onthe message, the first frequency band being non-overlapping with thesecond frequency band, and a duration of the first timeslot beinggreater than a duration of the second timeslot.

In another exemplary aspect, a method for enabling connectivity over adisadvantaged link is disclosed. The method includes performing, by afirst node of a plurality of nodes in a first frequency band in a firsttimeslot, one or more communications with at least a second node of theplurality of nodes; receiving, by the first node from at least thesecond node of the plurality of nodes in a second frequency band, alocal probe; receiving, by the first node from a destination node in thesecond frequency band in a second timeslot, a probe; computing, based onthe one or more communications, the probe and the local probe, a phasecorrection; and transmitting, to the destination node in the secondfrequency band, a message with the phase correction, the first frequencyband being non-overlapping with the second frequency band, and aduration of the first timeslot being greater than a duration of thesecond timeslot.

In yet another exemplary aspect, the above-described methods areembodied in the form of processor-executable code and stored in acomputer-readable program medium.

In yet another exemplary embodiment, a device that is configured oroperable to perform the above-described methods is disclosed.

The above and other aspects and their implementations are described ingreater detail in the drawings, the descriptions, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an example of a communication system that implementsembodiments of the disclosed technology.

FIG. 1B shows an example of performance of a loop antenna for mobile HFNIVIS communication.

FIGS. 2A and 2B show the stages of an exemplary embodiment for acollaborative downlink, in accordance with the disclosed technology.

FIG. 3A shows an example of time multiplexing for the collaborativedownlink.

FIG. 3B shows an example of frequency multiplexing for the collaborativedownlink.

FIG. 4 shows exemplary results of the capacity of the collaborativedownlink.

FIGS. 5A-5D show the stages of an exemplary embodiment for acollaborative uplink, in accordance with the disclosed technology.

FIG. 6 shows exemplary results of the capacity of the collaborativeuplink.

FIG. 7 shows a flowchart of an exemplary method for collaborativecommunication, in accordance with embodiments of the disclosedtechnology.

FIG. 8 shows a flowchart of another exemplary method for collaborativecommunication, in accordance with embodiments of the disclosedtechnology.

FIG. 9 is a block diagram representation of a portion of a radio thatmay be used to implement embodiments of the disclosed technology.

DETAILED DESCRIPTION

A mobile ad hoc network (MANET) is a continuously self-configuring,infrastructure-less network of mobile devices connected wirelessly. AMANET typically includes spatially-distributed, single-antenna,power-limited radio nodes, which may be both terrestrial andnon-terrestrial. In an example, the network may be dynamic (nodes aremoving), and may not be fully connected (multiple hops may be needed forfull network coverage). In another example, the radios may operate inmultipath fading propagation environments, and may employconstant-envelope (CE) modulations for increased power efficiency. Inyet another example, the network may communicate with a remote (ordestination) node that is otherwise unreachable by a single local radioor even by multiple radios transmitting simultaneously in aphase-incoherent manner.

FIG. 1A shows an example of a high-frequency (HF) communication system,which typically uses frequencies between 3 MHz and 30 MHz. Because radiowaves in this band can be reflected back to Earth by the ionospherelayer in the atmosphere a method known as “skip” or “skywave”propagation these frequencies are suitable for long-distancecommunication across intercontinental distances and for mountainousterrains which prevent line-of-sight (LOS) communications. In anexample, an HF communication is characterized by a sky wave rather thana ground wave being able to propagate from a transmitter to a receiver,and is referred to as HF near-vertical incident skywave (HF-NVIS)communications.

Section headings are used in the present document to improve readabilityof the description and do not in any way limit the discussion orembodiments (and/or implementations) to the respective sections only.

Difficulties of Mobile HF Communications

HF communications are typically used by radio amateurs (ham radiooperators) and for military communications, and especially in thetropics. The radio waves travel near-vertically upwards into theionosphere, where they are refracted back down and can be receivedwithin a circular region up to 650 km from the transmitter. If thefrequency is too high (that is, above the critical frequency of theionospheric F layer, shown in FIG. 1), refraction fails to occur and ifit is too low, absorption in the ionospheric D layer may reduce thesignal strength.

Typical HF antennas configurations include a horizontally polarized(parallel with the surface of the earth) radiating element that is from1/20th wavelength (λ) to ¼th λ, above the ground (for a nominal 10 MHzfrequency, 1/20λ≈5 ft and ¼λ≈25 ft). That proximity to the ground forcesthe majority of the radiation to go straight up. Overall efficiency ofthe antenna can be increased by placing a ground wire slightly longerthan the antenna parallel to and directly underneath the antenna.

The size of the typical HF antenna makes mobile HF communications fairlycumbersome. The efficacy is further impacted by time-varying frequencyavailability due to changing ionospheric conditions (e.g., dayionosphere vs night ionosphere shown in FIG. 1), limited transmissionpower due to electromagnetic interference (EMI) considerations, andsmall antennas being relatively lossy.

FIG. 1B shows an example of performance of a loop antenna for mobile HFcommunication (e.g., used by the mobile soldier 121 in FIG. 1A) with a 3ft diameter and 10 W (40 dBm) input power. As shown in FIG. 1B, for anominal frequency of 5 MHz, a bandwidth of 6 kHz results in the antennaoperating with −15 dB efficiency, producing an output power of only 25dBm. Typically, a vehicular antenna (e.g., used by the vehicle 131 inFIG. 1A) operating at 150 W input power has an efficiency that is 6 dBgreater than the loop antenna described in the context of FIG. 1B.

For the nominal mobile and vehicular nodes shown in FIG. 1A (and using,for example, the antenna described in FIG. 1B), point-to-point reliablecommunication rates are very low, e.g., voice transmissions at 2.4 kbpsare only possible in benign ionospheric conditions. Embodiments of thedisclosed technology advantageously enable collaboration between themobile network nodes (e.g., nodes 121 and 122 in FIG. 1A) to overcomethe inefficiencies of the disadvantaged HF link for both downlink anduplink communications. The mobile nodes can be configured to performlocal communications over a frequency band distinct from the frequencyband used for the HF link. In an example, the local communications forthe collaborative downlink may be performed using VHF (operating in30-300 MHz), UHF (operating in 300 MHz to 3 GHz), L-band (operating in1-2 GHz) or S-band (operating in 2-4 GHz). In the case of thecollaborative uplink (also referred to as collaborative beamforming),the VHF frequency band is used for the local communication network.

Exemplary Embodiments of a Collaborative Downlink

Embodiments of the disclosed technology provide methods for localconnected nodes that receive the same message over different channels,and subsequently collaborate to operate as a distributed multi-antennareceiver. In an example, the collaboration includes each mobile nodeperforming their own decoding operation and then exchangingsoft-decisions.

FIGS. 2A-2B show the two stages of an exemplary embodiment for acollaborative downlink, in accordance with the disclosed technology.

FIG. 2A shows an example of the first broadcast stage, wherein thedisadvantaged HF downlink is used to broadcast a message from the sourcenode (e.g., the vehicular node 131 in FIG. 1A) destination to each ofthe mobile nodes (e.g., nodes 121 and 122 in FIG. 1A, and shaded grey inFIG. 2A). In some embodiments, the source node (S) in FIG. 2A maygenerate the message that is broadcast. In other embodiments, the sourcenode may receive the message from a node outside the network (e.g., adrone or a satellite). In yet other embodiments, the message may bereceived from a backbone-type network (e.g., a high-speed opticalnetwork) distinct from the HF and L-band (or VHF or S-band) networks.

FIG. 2B shows an example of the second message-sharing stage, whereineach of the mobile nodes first attempt to decode the message receivedfrom the destination node over the disadvantaged HF link in the firststage (shown in FIG. 2A). The mobile nodes then distribute reliabilitymetrics (e.g., quantized log-likelihood ratios (LLRs)) using the L-bandnetwork such that each of the nodes receives collaboration messages fromthe other nodes. Each of the nodes now perform a second attempt todecode the message using the original reception as well as thereliability metrics that were exchanged in this stage.

In some embodiments, the distribution of the reliability metrics isperformed using a round-robin protocol, wherein the LLRs are transmittedone node at a time based on the ranking of quality metrics (e.g., basedon the first round of decoding). In an example, the quality metric maybe a symbol error rate (SER), a bit error rate (BER), a signal-to-noiseratio (SNR) or a signal-to-interference plus noise ratio (SINR). Inanother example, the quality metrics may be based on the output of anequalizer or an FEC decoder. In other embodiments, the mobile nodes maysimultaneously and synchronously transmit explicit LLRs or incorrecthard decisions.

FIG. 3A shows an example of time multiplexing for the collaborativedownlink. As shown therein, the downlink data is transmitted over theT_(D) sec timeslot, which is substantially longer than the T_(C) sectimeslot used for the collaboration messages. In an example, 10 kbps maybe supported on the data downlink with T_(D)=100 msec, and thecollaboration messages are communicated at 8 Mbps with T_(C)=0.5 msec,which corresponds to a 4% collaboration overhead when there are 8 mobilenodes. In another example, the time multiplexing scheme may be used whenthe reliability metrics are distributed using the round-robin protocoldescribed above.

FIG. 3B shows an example of frequency multiplexing for the collaborativedownlink. As shown therein, the downlink data is transmitted over afirst bandwidth (denoted F_(D)) and the collaboration messages arecommunicated between the mobile nodes over a second bandwidth (denotedF_(C)) that is non-overlapping with the first bandwidth. In thefrequency multiplexing scenario, the collaboration messagescorresponding to a first data message may be exchanged (over F_(C))concurrently with the reception of a second data message (over F_(D)).

FIG. 4 shows exemplary results of the collaborative downlink capacity,wherein the 99% outage capacity (in kilobits per sec, kpbs) is plottedas a function of the number of collaborating nodes, and assumes that thenetwork nodes are spread over a distance of 1 km, and the vehicular nodeuses a center frequency of 4 MHz, a transmit power of 50 dBm and anantenna gain of −12 dBi. The 99% outage capacity is plotted for acoherence distance (d_(coh)) of 250 m and 1 km, wherein the coherencedistance is defined as the distance between network nodes over which thechannels for two nodes remain at least 75% correlated. As shown in FIG.4, there is an almost 100× improvement in capacity when 10 nodescollaborate in the worst correlation conditions.

Exemplary Embodiments of a Collaborative Uplink

Embodiments of the disclosed technology provide methods of phaseadjustment for enabling distributed beamforming in relevant scenarioswith real-world radio constraints, RF degradations and multipathpropagation. Furthermore, local mechanisms for data sharing andcollaborative transmission with coarse timing synchronization across theradios, which are typically available in different wireless networkingtechnologies, are leveraged.

The present document describes distributed collaborative beamformingfrom a set of spatially-distributed radio network nodes N_(i); i=1, 2, .. . , K, towards a remote collaborating radio destination node D. Insome embodiments, a method for distributed collaborative beamforming ina network comprising multiple network nodes (or nodes, or radios)comprises four stages.

Stage 1. Each network node gets possession of a common message sent by asource S, which is the message to be beam-formed towards the destinationD.

Stage 2. The network nodes self-cohere via a sequence of bidirectionalsignal exchanges (or a combination of signal and message exchanges),performed between chosen pairs of nodes. This results in all nodes inthe network having been included in the self-coherence process andhaving derived and stored a phase correction value.

Stage 3. Each network node receives a broadcast probe signal from thedestination node D. Based on this probe, each network node estimates acomplex-valued, multipath-fading baseband channel model, identifies thestrongest tap in the channel model, and computes the phase (argument) ofthe strongest complex-valued tap. In some embodiments, all the networknodes receive the probe from the destination at roughly the same time(e.g., within a timeslot, or within adjacent timeslots).

Stage 4. Each network node quasi-synchronously (e.g., within apre-defined turn-around time upon destination-probe reception) transmitsthe common message with a total correction phase added to the phase(argument) of the complex baseband values representing the informationstream (of the common message). The total correction phase is equal tothe negative of the sum of the node's phase correction value (as derivedin Stage 2) and the phase (argument) of the strongest complex-valued tap(as estimated in Stage 3).

In some embodiments, and for constant-envelope modulated signals,baseband phase correction can be implemented simply by an index shiftinto the look-up table that generates the information carrying digitalphase sequence, thereby maintaining the constant envelope property forthe transmitted signal.

In some embodiments, a network node may perform the four stages in anorder different from that described above, as long as Stage 4 (whichincludes the actual beamforming operation) is performed last. Forexample, the network node may first receive a probe from the destinationand compute the phase of the strongest tap of the channel estimation(Stage 3), then receive the common message (Stage 1), followed byparticipating in the self-coherence process with the other network nodesto derive its phase correction value (Stage 2), and finally perform thebeamforming operation (Stage 4). For another example, the network nodemay first participate in the self-coherence process with the othernetwork nodes to derive its phase correction value (Stage 2), thenreceive a probe from the destination and compute the phase of thestrongest tap of the channel estimation (Stage 3), followed by receivingthe common message (Stage 1), and finally perform the beamformingoperation (Stage 4).

In some embodiments, the four-stage process described above produces acomposite (co-transmitted, superimposed) signal at the destination nodewhich has a larger signal-to-noise ratio (SNR) than what would have beenreceived had the nodes co-transmitted in a phase-incoherent manner,thereby producing a distributed beamforming gain.

In some embodiments, the four-stage process described above can beadapted to simultaneously distribute the common message to multipledestinations.

FIGS. 5A-5D show the four stages of an exemplary embodiment for acollaborative uplink, in accordance with the disclosed technology.

FIG. 5A shows an example of the first message-sharing stage, wherein theK network nodes (shaded grey) get possession of a common message from asource (S). In some embodiments, the message can be distributed viabroadcast transmission by one of the network nodes (which also acts asthe source in this first stage). In other embodiments, it may bebroadcast by a source outside the network of K nodes (e.g., a drone or asatellite broadcasting this common message to a terrestrial network sothat this network may further relay the message to D, otherwiseunreachable by the source). In yet other embodiments, it may be sharedvia a backbone-type network (e.g., a high-speed optical network)distinct from the radio network.

FIG. 5B shows an example of the second self-coherence stage. In someembodiments, the purpose of the self-coherence process is to produce thematrix ΔØ={δØ_(ij)}; i≠j; i,j=1, 2, . . . , K, whereδØ_(ij)=2(∂_(i)−∂_(j)), where ∂_(i) is the phase of the free-running,carrier-producing oscillator of radio node N_(i). By definition,δØ_(ii)=0 for any i. In an example, and as shown in FIG. 2B, this isachieved through a sequence of bi-directional probe-signal exchanges (orsignal and message exchanges) between pairs of nodes (i,j).

Once the matrix ΔØ has been computed fully, a selection processidentifies a proper column with desirable characteristics. The column isindexed by the so-called reference node N_(r), e.g., the column[δØ_(1r), δØ_(2r), . . . , δØ_(Kr)] is computed and stored at each node.The values δØ_(ir), i=1, 2, . . . , K, comprise the set of requiredcorrection phases that are used in the beamforming stage (Stage 4).

In some embodiments, the matrix ΔØ is computed by electing a priori areference node, and computing only the reference column [δØ_(1r),δØ_(2r), . . . , δØ_(Kr)].

In other embodiments, the matrix ΔØ is computed by performing around-robin computation, starting from a chosen start node andproceeding sequentially, whereby each node i in the sequence selects itspaired node j on the basis of the highest SNR from all links connectedto it, the same is repeated by j, provided that the next selected pairnode has not already been already covered before, and so on, until allnodes are exhausted. In another example, other link metrics (e.g., thehighest signal-to-interference-plus-noise ratio (SINR)) may be used toselect the next paired node.

In yet other embodiments, some entries of the matrix ΔØ may bedetermined via the use of the identities 2Δθ_(ij)=−2Δθ_(ji) and2Δθ_(ij)=2Δθ_(ik)+2Δθ_(kj) (the latter named the “triangle identity”).Alternatively, all entries in ΔØ are computed using the said identitiesplus an estimate of the quality (error variance) of the estimated valueδØ_(ij).

For the computation of the matrix ΔØ in the embodiments described above,neither a fully-connected network (e.g., radio nodes in multiple hopsmay participate) nor a static network (e.g., dynamic phase tracking maybe included in the computation) is required. In some embodiments, thevalue δØ_(ij) can be computed in one of two ways: either via purebidirectional exchanges of signals or via a mixture of signal exchangesand message exchanges.

Bidirectional signal exchanges. In some embodiments, a purebidirectional exchange between nodes N_(i) and N₁ includes the nodeN_(i) first emitting a signal, e.g., a probe akin to a tone, i.e. s_(i)^(pb)(t)=cos(2πf_(c)t+∂_(i)).

In complex-envelope notation, the tone s_(i) ^(pb)(t)=Re{e^(j∂) ^(i)e^(j2πf) ^(c) ^(t)} and the complex envelope is {tilde over (s)}_(i)^(pb)(t)=e^(j∂) ^(i) . A transmission induces a positive phase shift of∂_(i) to the transmitted carrier cos(2πf_(c)t). Correspondingly, thereceiver of node N_(j) mixes the incoming signal withcos(2πf_(c)t+∂_(j)), and thus any reception equivalently subtracts thelocal phase ∂_(j). Neglecting the channel gain scaling, the interveningnarrowband channel multiplies with the phasor

e^(j∂_(i → j)^(ch)),therein adding the random-variable phase of ∂_(i→j) ^(ch), and the totalphase at the receiver node N_(j) is θ_(i→j) ^(total)=∂_(i)+∂_(i→j)^(ch)−∂_(j).

In this exemplary pure bi-directional exchange, node N_(j) produces, atbaseband, the negative of the total phase −θ_(i→j)^(total)=−∂_(i)−∂_(i→j) ^(ch)+∂_(j) (referred to as “conjugation” or“phase reversal”). Upon up-conversion (which adds the phase ∂_(j)),propagation through the reciprocal channel (which adds the phase ∂_(i→j)^(ch) and thus cancels the term −∂_(i→j) ^(ch)) and down-conversion atnode N_(i) (which subtracts the phase ∂_(i)), the total phase at theradio baseband of node N_(i) is θ_(i→j) ^(total)=(−∂_(i)−∂_(i→j)^(ch)+∂_(j))+∂_(j)+∂_(i→j) ^(ch)−∂_(i)=2(∂_(j)−∂_(i))=−θØ_(ij).

In some embodiments, node N_(j) can be informed of this value throughthe messaging protocol. In other embodiments, node N_(j) can initiateits own bidirectional exchange with node N_(j) in order to computeδØ_(ji).

Although, in principle, δØ_(ji)=−δØ_(ij), in practice, such estimatesmay be noisy. In some embodiments, the network protocol may allow formessage exchanges between nodes, and a better estimate of δØ_(ij) can bemade by both nodes by averaging the individual estimates.

Message and signal exchanges. In some embodiments, a mixture of signaland message exchanges includes the node N_(i) initiates the emission ofa probe, as before, and node N_(j) computes θ_(i→j)^(total)=∂_(i)+∂_(i→j) ^(ch)−∂_(j), as described above. In thisembodiment, Node N_(j) sends, to node N_(i), an information-carryingmessage containing this computed value of θ_(i→j) ^(total).Contemporaneously with this message, node N_(j) emits a probe signal, sothat node N_(i) can in turn compute the phase θ_(j→i)^(total)=∂_(j)+∂_(j→i) ^(ch)−∂_(i). Under the assumption of channelreciprocity, ∂_(i→j) ^(ch)=∂_(j→i) ^(ch). Thus, node N_(i) possessesknowledge of θ_(i→j) ^(total) as well as θ_(j→i) ^(total) and can easilyinfer that θ_(i↔j) ^(total)=θ_(j→i) ^(total)−θ_(i→j) ^(total)=−δØ_(ij).

In some embodiments, and as described in the context of bidirectionalsignal exchanges, the nodes can repeat that process by now starting fromN_(j), or can share the estimated value of δØ_(ij) via messaging.

FIG. 5C shows an example of the third per-node phase estimation stage.In some embodiments, the destination node (D) broadcasts a probe, andeach of the network nodes computes a tap-spaced, complex-valued basebandchannel model in response to receiving the probe from the destinationnode. At each node, the magnitudes of the estimated taps are comparedand the largest is selected, and then used to compute an argument(phase) estimate ∂_(i) ^(str_tap) for each node i=1, 2, . . . , K.

FIG. 5D shows an example of the fourth destination beamforming stage. Insome embodiments, the transmission from node N_(i) is performed with atotal correction phase given by ∂_(i) ^(total_corr)=−∂_(i)^(str_tap)−δØ_(ir).

In some embodiments, the distributed collaborative beamforming processdescribed in the context of FIGS. 5A-5D results in the destination nodeD receiving a multitude of taps. The taps arriving at D include (i)those that have been subjected to the processing of Stage 3 and havebeen subsequently transmitted with the proper phase ∂_(i) ^(total_corr)from each node N_(i), and (ii) all the remaining taps which have notbeen processed as per Stage 3 (namely, all taps except the selectedstrongest). All selected and processed taps contributing to thesuperimposed (co-transmitted) baseband channel model at the destinationnode D are in principle phase-aligned, with a common complex-basebandargument (phase) equal to δØ_(rD), thus producing a coherent beamforminggain modulo δØ_(rD). The remaining non-selected and non-processedchannel taps coming from all nodes and contributing to the superimposedchannel at D act as noncoherent taps and do not provide beamforminggain, although they provide noncoherent power gains.

In some embodiments, the self-coherence process (Stage 2) may beimplemented between the network nodes using the VHF-band channel (e.g.,the collaboration slots in FIG. 3A or the second bandwidth (F_(C)) inFIG. 3B), the remote destination node may broadcast a probe over the HFchannel that is received by the nodes and used to compute the strongesttap of a channel estimate (Stage 3), and the nodes could finally performthe beamforming over the HF channel in order to transmit a commonmessage to the remote destination node (Stage 4). In an example, theremote destination may be a seafaring vessel in the littoral zone andthe network nodes may be members of a landing party.

Embodiments of the disclosed technology can support distributedcollaborative beamforming in a dual-channel framework by ensuring thetotal correction phase for beamforming (Stage 4) is computed for the HFcommunication channel, even though the VHF-band is used when performingthe self-coherence process (Stage 3). The term is derived based on theprobe from D and is with respect to the HF channel, but the term isderived using the VHF-band self-coherence process, and must be convertedto the HF band to ensure the correct computation of the total correctionphase.

In some embodiments, the term δØ_(ir) is derived for the HF (or HF-NVIS)band by ensuring that the VHF-band and HF-band oscillators arephysically coupled in the radios. In other embodiments, the nodes coulduse the ground wave of any HF communication to perform theself-coherence process.

FIG. 6 shows exemplary results of the capacity of the collaborativeuplink, wherein the 99% outage capacity (in kilobits per sec, kpbs) isplotted as a function of the number of collaborating nodes, and assumesthat the network nodes are spread over a distance of 1 km, and each nodeuses a center frequency of 4 MHz, a transmit power of 40 dBm and anantenna gain of −25 dBi. Similar to FIG. 4, the 99% outage capacity isplotted for a coherence distance (d_(coh)) of 250 m and 1 km. As shownin FIG. 6, there is an almost 1000× improvement in capacity when 10nodes collaborate in the worst correlation conditions.

Additional Exemplary Embodiments of the Presently Disclosed Technology

In some embodiments, all the network nodes are fully connected. Theselection of a reference node, which completes Stage 2 with all nodesindividually, may be performed in a sequence of its choice, since allnodes are within hearing range of the reference node. The choice of thereference node may pertain to the best average link SNR (averaged overall other nodes). More generally, any function (e.g., average, median,maximum, etc.) of a link-quality metric (e.g., SNR, SINR, etc.) may beused in the determination of the choice of the network node. It isfurther assumed, in this embodiment, that link-quality information isavailable to all nodes which share it and update it regularly.

In some embodiments, the reference node may have good access to some butnot all the nodes of the network due to some low-quality links. Thereference node may identify such impaired-link nodes and request, viaproper messages, the help of neighboring nodes (e.g., send a requestthat they perform bidirectional exchanges with the impaired-link nodesin more favorable link conditions and thus assist in completing the fullreference column via the said identities).

In some embodiments, there may be information on the nature of links(e.g., line-of-sight (LoS) or non-LoS (NLoS)), which may be used todetermine which links are to be used by each node in its ownbidirectional exchanges (e.g., only the LoS links may be used), in theprocess of filling out the phase matrix.

In some embodiments, an initial node may be chosen either at random, orvia a quality metric (e.g., best link SNR among nodes), and is referredto as “node 1”. Node 1 completes δØ₁₂ with a second node (“node 2”),which may be the node within hearing range of node 1 with the highestlink SNR of all links out of node 1. The pair (1,2) is announced via ashort message, so that all nodes in the network know which pairs havebeen covered. Then node 2 completes δØ₂₃ with a subsequent node (“node3”), chosen in a similar manner as before, and the pair is announced,and so on. The process ends when all nodes within hearing range (e.g.,one-hop nodes) have been completed. If there are nodes within hearingrange in some portion of the network (e.g., in a network of at least 2hops), then a node from the second hop requests participation to theself-coherence process. The node(s) which hear it extend the process tothat node, which then completes the process for those in the second-hophearing range, and the process repeats until all hops have been covered.Thus, distributed collaborative beamforming can be applied to multi-hop(and not fully connected) networks, provided that the whole multi-hopnetwork is within range of the probe of destination D for the subsequentstages.

In some embodiments, the estimate of the individual terms δØ_(ij) may beaccompanied by a quality metric, signifying the confidence of theestimating node on the quality of the said term (e.g., an estimatederror variance). The various quality metrics may be distributed inmessage exchanges and used subsequently to refine estimates either viathe use of identities (such as the triangle identity) when completingthe matrix ΔØ, namely by incorporating weighting terms in thecomputation, or in refining final estimates of reciprocal links ((i→j)and (j→i)), assuming that the protocol allows computation of both. Thefinal quality metrics for all relevant phase-difference qualities may beused for selecting the reference node, e.g., as the one whose columnpossesses the highest average quality metric. Links for which thequality of the estimate δØ_(ij) is deemed unacceptable (too noisy) maydiscard the estimate and another sequence of nodes in the computationprocess may be selected.

In some embodiments, individual links may be subjected to significantinterference (e.g., due to jamming). The elements of the matrixcorresponding to such corrupted links may be eliminated from thebidirectional signal exchange (phase measurement) process. Instead, thesaid elements may be filled in via other measurements in relateduncorrupted links and the use of the aforementioned identities (e.g.,the triangle identity).

In some embodiments, the network nodes may use separate oscillatorphases for the transmit and receive modes.

In some embodiments, the terms δØ_(ij) are computed not just bybidirectional signal exchanges between nodes but by a mixture of signalexchanges as well as message exchanges, whereby the messages convey the(quantized) value of the estimated baseband phase of the radio that hasreceived a signal and has computed such a phase. The final estimate ofδØ_(ij) is computed by proper combination of the signal phases as wellas the massage-conveyed phase values.

In some embodiments, the terms δØ_(ij) are estimated viaparameter-tracking methods which account for mobility and phase-noiseimpairments. Such phase-tracking methods can also be used to fill in(e.g. by prediction) estimated values in case the process is interruptedfor a short period of time. In an example, these tracking methods canalso be used to reduce the frequency for bidirectional exchanges, thuslowering the network overhead traffic necessary to support theembodiments described in the present document.

In some embodiments, a variety of methods in may be employed in choosingthe strongest channel tap for computing the respective phase. In anexample, the strongest channel tap is the direct largest gain valueamong taps. In another example, a complex channel tap is computed viainterpolation methods between taps estimated using the observationsamples (measurements) of the channel-estimation process.

In some embodiments, each of the mobile nodes (e.g., 121 and 122 in FIG.1A) is configured to support a dual-channel radio, which is typicallydefined as two distinct radios inside a common mechanical enclosure. Foran exemplary downlink, one of the first two radios is dedicated to theHF communication link and the second of the two radios operates overeither the VHF, UHF, L-band or S-band. For an exemplary uplink, thefirst and second radios support the HF and VHF communication links,respectively. The methods described in this document may be implementedin dual-channel radios by leveraging existing communication lines(physical wired connections) between the two baseband processors, FPGAs,GPPs, etc., of each of the two radios in order to exchange thecollaboration messages. In an example, a dual-channel radio can beconfigured to use the time multiplexing scheme or frequency multiplexingscheme shown in FIGS. 3A and 3B, respectively.

In some embodiments, each of the mobile nodes (e.g., 121 and 122 in FIG.1A) is configured to support two physically separated radios connectedby a wired (e.g., Ethernet) or wireless (e.g., local Wi-Fi link)connections.

Methods for Collaborative Uplink and Downlink Communication

FIG. 7 shows a flowchart of an example of a method 700 enablingconnectivity over a disadvantaged link operating in a first frequencyband. The method 700 includes, at operation 710, receiving, by a firstnode of a plurality of nodes from a source node in the first frequencyband in a first timeslot, a first signal comprising a message.

The method 700 includes, at operation 720, receiving, by the first nodefrom at least a second node in a second frequency band in a secondtimeslot, a second signal that is used to generate a first reliabilitymetric corresponding to the message.

The method 700 includes, at operation 730, performing, based on aplurality of reliability metrics corresponding to the message and thefirst reliability metric, a processing operation on the message, thefirst frequency band being non-overlapping with the second frequencyband, and a duration of the first timeslot being greater than a durationof the second timeslot.

In some embodiments, the method 700 further includes the operation ofgenerating, based on performing the processing operation on the message,the plurality of reliability metrics.

In some embodiments, the method 700 further includes the operation oftransmitting, by the first node in the second frequency band, a thirdsignal comprising a second reliability metric of the plurality ofreliability metrics.

In some embodiments, the first reliability metric is based on combiningmultiple partial reliability metrics.

In some embodiments, the first frequency band is a high-frequency (HF)band, and wherein a center frequency of the second frequency band isgreater than a center frequency of the first frequency band.

In some embodiments, the second frequency band is a ultra-high-frequency(UHF) band, a very-high-frequency (VHF) band, an S-band or an L-band.

In some embodiments, the processing operation comprises at least one ofan equalization operation, a data detection operation or an FEC decodingoperation.

In some embodiments, the processing operation further comprises at leastone of generating a channel response for the disadvantaged link,estimating a frequency offset of the disadvantaged link or updating oneor more equalizer taps in the equalization operation.

FIG. 8 shows a flowchart of an example of a method 800 enablingconnectivity over a disadvantaged link operating in a first frequencyband. The method 800 includes, at operation 810, performing, by a firstnode of a plurality of nodes in a first frequency band in a firsttimeslot, one or more communications with at least a second node of theplurality of nodes.

The method 800 includes, at operation 820, receiving, by the first nodefrom at least the second node of the plurality of nodes in a secondfrequency band, a local probe.

The method 800 includes, at operation 830, receiving, by the first nodefrom a destination node in the second frequency band in a secondtimeslot, a probe.

The method 800 includes, at operation 840, computing, based on the oneor more communications, the probe and the local probe, a phasecorrection.

The method 800 includes, at operation 850, transmitting, to thedestination node in the second frequency band, a message with the phasecorrection, the first frequency band being non-overlapping with thesecond frequency band, and a duration of the first timeslot beinggreater than a duration of the second timeslot.

In some embodiments, the method 800 further includes the operation ofreceiving information corresponding to the message from (a) a third nodeof the plurality of nodes, (b) a backbone-type network or (c) a sourcenode that is different from each of the plurality of nodes.

In some embodiments, the one or more communications comprises abi-directional communication that is performed with each of theplurality of nodes.

In some embodiments, the first frequency band is a very-high-frequency(VHF) band, and wherein the second frequency band is a high-frequency(HF) band.

In some embodiments, communication in the first frequency band uses afirst transceiver, communication in the second frequency band uses asecond transceiver, and a local oscillator of the first transceiver iscoupled to a local oscillator of the second transceiver. In an example,the coupling of the two oscillators may use a master-slaveconfiguration, which ensures that the oscillators are kept synchronizedin order to implement the correct phase to achieve collaborative uplinkcommunication.

FIG. 9 is a block diagram representation of a portion of a radio, inaccordance with some embodiments of the presently disclosed technology.A radio 911 can include processor electronics 901 such as amicroprocessor that implements one or more of the techniques presentedin this document. The radio 911 can include transceiver electronics 903to send and/or receive wireless signals over one or more communicationinterfaces such as antenna(s) 909. The radio 911 can include othercommunication interfaces for transmitting and receiving data. Radio 911can include one or more memories 907 configured to store informationsuch as data and/or instructions. In some implementations, the processorelectronics 901 can include at least a portion of the transceiverelectronics 903. In some embodiments, at least some of the disclosedtechniques, modules or functions (including, but not limited to, methods700 and 800) are implemented using the radio 911.

Some of the embodiments described herein are described in the generalcontext of methods or processes, which may be implemented in oneembodiment by a computer program product, embodied in acomputer-readable medium, including computer-executable instructions,such as program code, executed by computers in networked environments. Acomputer-readable medium may include removable and non-removable storagedevices including, but not limited to, Read Only Memory (ROM), RandomAccess Memory (RAM), compact discs (CDs), digital versatile discs (DVD),etc. Therefore, the computer-readable media can include a non-transitorystorage media. Generally, program modules may include routines,programs, objects, components, data structures, etc. that performparticular tasks or implement particular abstract data types. Computer-or processor-executable instructions, associated data structures, andprogram modules represent examples of program code for executing stepsof the methods disclosed herein. The particular sequence of suchexecutable instructions or associated data structures representsexamples of corresponding acts for implementing the functions describedin such steps or processes.

Some of the disclosed embodiments can be implemented as devices ormodules using hardware circuits, software, or combinations thereof. Forexample, a hardware circuit implementation can include discrete analogand/or digital components that are, for example, integrated as part of aprinted circuit board. Alternatively, or additionally, the disclosedcomponents or modules can be implemented as an Application SpecificIntegrated Circuit (ASIC) and/or as a Field Programmable Gate Array(FPGA) device. Some implementations may additionally or alternativelyinclude a digital signal processor (DSP) that is a specializedmicroprocessor with an architecture optimized for the operational needsof digital signal processing associated with the disclosedfunctionalities of this application. Similarly, the various componentsor sub-components within each module may be implemented in software,hardware or firmware. The connectivity between the modules and/orcomponents within the modules may be provided using any one of theconnectivity methods and media that is known in the art, including, butnot limited to, communications over the Internet, wired, or wirelessnetworks using the appropriate protocols.

While this document contains many specifics, these should not beconstrued as limitations on the scope of an invention that is claimed orof what may be claimed, but rather as descriptions of features specificto particular embodiments. Certain features that are described in thisdocument in the context of separate embodiments can also be implementedin combination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesub-combination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asub-combination or a variation of a sub-combination. Similarly, whileoperations are depicted in the drawings in a particular order, thisshould not be understood as requiring that such operations be performedin the particular order shown or in sequential order, or that allillustrated operations be performed, to achieve desirable results.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this disclosure.

What is claimed is:
 1. A method for enabling connectivity over adisadvantaged link operating in a first frequency band, comprising:receiving, by a first node of a plurality of nodes from a source node inthe first frequency band in a first timeslot, a first signal comprisinga message; receiving, by the first node from at least a second node in asecond frequency band in a second timeslot, a second signal that is usedto generate a first reliability metric corresponding to the message; andperforming, based on a plurality of reliability metrics corresponding tothe message and the first reliability metric, a first processingoperation on the message, wherein the first frequency band isnon-overlapping with the second frequency band, and wherein a durationof the first timeslot is greater than a duration of the second timeslot.2. The method of claim 1, further comprising: generating, based onperforming a second processing operation on the message, the pluralityof reliability metrics.
 3. The method of claim 2, further comprising:transmitting, by the first node in the second frequency band, a thirdsignal comprising a second reliability metric of the plurality ofreliability metrics.
 4. The method of claim 1, wherein the firstreliability metric is based on combining multiple partial reliabilitymetrics.
 5. The method of claim 1, wherein the first frequency band is ahigh-frequency (HF) band, and wherein a center frequency of the secondfrequency band is greater than a center frequency of the first frequencyband.
 6. The method of claim 5, wherein the second frequency band is aultra-high-frequency (UHF) band, a very-high-frequency (VHF) band, anS-band, or an L-band.
 7. The method of claim 1, wherein the firstprocessing operation comprises at least one of an equalizationoperation, a data detection operation, or a forward error correction(FEC) decoding operation.
 8. The method of claim 7, wherein the firstprocessing operation further comprises at least one of generating achannel response for the disadvantaged link, estimating a frequencyoffset of the disadvantaged link, or updating one or more equalizer tapsin the equalization operation.
 9. A method for enabling connectivityover a disadvantaged link operating in a first frequency band,comprising: performing, by a first node of a plurality of nodes in afirst frequency band in a first timeslot, one or more communicationswith at least a second node of the plurality of nodes; receiving, by thefirst node from at least the second node of the plurality of nodes in asecond frequency band, a local probe; receiving, by the first node froma destination node in the second frequency band in a second timeslot, aprobe; computing, based on the one or more communications, the probe andthe local probe, a phase correction; and transmitting, to thedestination node in the second frequency band, a message with the phasecorrection, wherein the first frequency band is non-overlapping with thesecond frequency band, and wherein a duration of the first timeslot isgreater than a duration of the second timeslot.
 10. The method of claim9, further comprising: receiving information corresponding to themessage from (a) a third node of the plurality of nodes, (b) abackbone-type network, or (c) a source node that is different from eachof the plurality of nodes.
 11. The method of claim 9, wherein the one ormore communications comprises a bi-directional communication that isperformed with each of the plurality of nodes.
 12. The method of claim9, wherein the first frequency band is a very-high-frequency (VHF) band,and wherein the second frequency band is a high-frequency (HF) band. 13.The method of claim 12, wherein communication in the first frequencyband uses a first transceiver, wherein communication in the secondfrequency band uses a second transceiver, and wherein a local oscillatorof the first transceiver is coupled to a local oscillator of the secondtransceiver.
 14. An apparatus for enabling connectivity over adisadvantaged link operating in a first frequency band, comprising: aprocessor; and a memory with instructions thereon, wherein theinstructions upon execution by the processor cause the processor to:receive, by a first node of a plurality of nodes from a source node inthe first frequency band in a first timeslot, a first signal comprisinga message, receive, by the first node from at least a second node in asecond frequency band in a second timeslot, a second signal that is usedto generate a first reliability metric corresponding to the message, andperform, based on a plurality of reliability metrics corresponding tothe message and the first reliability metric, a first processingoperation on the message, wherein the first frequency band isnon-overlapping with the second frequency band, and wherein a durationof the first timeslot is greater than a duration of the second timeslot.15. The apparatus of claim 14, wherein the instructions upon executionby the processor further cause the processor to: generate, based onperforming a second processing operation on the message, the pluralityof reliability metrics.
 16. The apparatus of claim 15, wherein theinstructions upon execution by the processor further cause the processorto: transmitting, by the first node in the second frequency band, athird signal comprising a second reliability metric of the plurality ofreliability metrics.
 17. The apparatus of claim 14, wherein the firstreliability metric is based on combining multiple partial reliabilitymetrics.
 18. The apparatus of claim 14, wherein the first frequency bandis a high-frequency (HF) band, and wherein a center frequency of thesecond frequency band is a greater than a center frequency of the firstfrequency band.
 19. The apparatus of claim 18, wherein the secondfrequency band is a ultra-high-frequency (UHF) band, avery-high-frequency (VHF) band, an S-band, or an L-band.
 20. Theapparatus of claim 14, wherein the first processing operation comprisesat least one of an equalization operation, a data detection operation, aforward error correction (FEC) decoding operation, generating a channelresponse for the disadvantaged link, estimating a frequency offset ofthe disadvantaged link, or updating one or more equalizer taps in theequalization operation.